2016-05-20 14:15 GMT+03:00 Richard Biener <richard.guent...@gmail.com>: > On Fri, May 20, 2016 at 11:44 AM, Ilya Enkovich <enkovich....@gmail.com> > wrote: >> 2016-05-20 12:24 GMT+03:00 Richard Biener <richard.guent...@gmail.com>: >>> On Thu, May 19, 2016 at 9:40 PM, Ilya Enkovich <enkovich....@gmail.com> >>> wrote: >>>> Hi, >>>> >>>> This patch extends vectorizer cost model to include masking cost by >>>> adding new cost model locations and new target hook to compute >>>> masking cost. >>> >>> Can you explain a bit why you add separate overall >>> masking_prologue/body_cost rather >>> than using the existing prologue/body cost for that? >> >> When I make a decision I need vector loop cost without masking (what >> we currently >> have) and with masking (what I add). This allows me to compute >> profitability for >> all options (scalar epilogue, combined epilogue, masked epilogue) and choose >> one >> of them. Using existing prologue/body cost would allow me compute masking >> profitability with no fall back to scalar loop profitability. > > Yes, but for this kind of purpose you could simply re-start > separate costing via the init_cost hook?
But that would require double scan through loop statements + double profitability estimations. I compute masking cost during statements analysis (see patch #05) in parallel with regular costs computations. Note that masking costs is a cost of masking only. Thus cost of a vector masked iteration is body cost + body masking cost. > >>> I realize that the current vectorizer cost infrastructure is a big >>> mess, but isn't it possible >>> to achieve what you did with the current add_stmt_cost hook? (by >>> inspecting stmt_info) >> >> Cost of a statement and cost of masking a statement are different things. >> Two hooks called for the same statement return different values. I can >> add vect_cost_for_stmt enum elements to cover masking but I thought >> having stmt_masking_cost would me more clear. > > I agree we need some kind of overloading and I'm not against a separate hook > for this. On a related note what is "masking cost" here? I could imagine > that masking doesn't unconditionally add a cost to a stmt but its execution > cost may now depend on whether an element is masked or not. > > Does the hook return the cost of the masked stmt or the cost of masking > the stmt only (so you need to do add_stmt_cost as well on the same stmt)? It returns the cost of masking the statement only. Thus if a hardware has no penalty for executing masked instruction then return value should be 0. Thanks, Ilya > > Thanks, > Richard. > >> Thanks, >> Ilya >> >>> >>> Richard. >>> >>>> Thanks, >>>> Ilya
